A cardiac arrest is a disruption of the heart""s functioning that causes a lack of blood flow to vital organs. The majority of cardiac arrests are associated with a heart arrhythmia such as ventricular fibrillation. During ventricular fibrillation, the normal rhythmic ventricular contractions are replaced by rapid and irregular twitching that results in ineffective and severely reduced pumping of the heart. One method of treating ventricular fibrillation is to use a defibrillator to administer shocks to a patient""s heart in order to restore the normal rhythmic ventricular contractions.
There are multiple types of defibrillators, each used for different purposes. Internal defibrillators are implanted in the patient and are used to prevent ventricular fibrillation and regulate the heart rhythms. External defibrillators are used by paramedics and hospitals in order to treat ventricular fibrillation after the occurrence of a heart attack. External defibrillators often have numerous additional features, such as smaller ECG units, that aid in treating the patient and evaluating the factors used in administering shocks. The external defibrillators can be fully automatic, semi-automatic, or manual, depending on the end operator. The more automatic a defibrillator, the greater the role of a controller within the defibrillator plays in administering treatment.
These defibrillators can be portable, such as those used by paramedics and EMS personnel, or attached to carts such as those found in clinics and hospitals. One such portable external defibrillator is disclosed in U.S. Pat. No. 6,141,584 to Rockwell et al., which is commonly assigned and the disclosure of which is incorporated herein by reference.
As shown in FIG. 1, a defibrillator system 1 includes a defibrillator 10 which administers a shock to the patient through paddles/electrodes 20. As shown in FIG. 2, the paddles 20 are connected to a connector 22 by leads 30. The connector 22 is inserted into socket 14 in order to deliver the charge from the defibrillator 10 to the paddles 20. In order to direct the defibrillator 10 to administer the shock, the operator presses a shock button 12 that is located on the defibrillator 10.
In addition, the defibrillator 10 also has a display 16 that is used by the operator to view ECG information or other information useful in the caring for and monitoring of the progress of the patient. The ECG information, which provides information on the condition of the patient""s heart, is received through the paddles 20 that also provide the shock to the patient. Since the shown the defibrillator 10 is portable, it has a battery charge indicator 18 so that the operator can assess the ability of the defibrillator 10 to continue to administer treatment to the patient.
In operation, when a patient goes into cardiac arrest, the electrodes 20 are applied across the chest of the patient in order to acquire the ECG signal from the patient""s heart. The ECG information is displayed to the operator on the display 16. In a manual defibrillator, the operator determines from the ECG information whether to administer the shock. For automatic and semiautomatic defibrillators, the defibrillator 10 aids in this determination to varying degrees.
However determined, if ventricular fibrillation is to be treated with the defibrillator system 1, the operator applies the paddles 20 to the patient and presses the shock button 12. The defibrillator administers the shock through the paddles 20 to the patient in order to restore the normal rhythm of the heart. The defibrillator 10 is then used to again assess the condition of the patient, and to administer further treatments based on the detected ECG signal. In general, only three such treatments are provided with any likelihood of success.
FIG. 3 is a schematic representation of the defibrillator 10. The paddles 20 provide an ECG signal to the ECG front end 102, which provides the ECG signal to a controller 106 for evaluation and display to the operator via a user interface 114. This information is also stored by the controller 106 in a memory 118. Also stored in the memory 118 is an event summary 130, in which information from an event mark 110, a microphone 112, and/or from a clock 116 are stored. This information is useful during a transfer (often called a handoff) between the hospital and the clinic in order to continue the treatment of the patient. In the device shown, an infrared communications port 120 is provided to communicate the information in memory 118 with an outside device during the transfer.
In addition, a power source 140 is provided in order to power the entire defibrillator 10. The power source 140 can be a line source or a battery, or any similar device which provides sufficient power to provide the shock and the ECG monitoring functions described herein. For portable defibrillators such as that shown, a battery is typically used for the power source 140. This battery may be disposable, or rechargeable.
A high voltage (HV) delivery device 108 administers the shock to the patient via the paddles 20 at the command of the controller 106. At the command of the operator using the shock button 12, the charge from the high voltage delivery device 108 is administered to the patient in order to bring about the normal rhythmic ventricular contractions. The power supply 140 supplies the charging energy to the high voltage delivery device 108 during a charging time in order to store sufficient energy to administer a treatment. This charging time is preferably small since the rapid administration of the treatments is desirable in order to produce a favorable result.
As schematically shown in FIG. 4, the high voltage delivery device 108 has two major components: a transformer 204 and a high voltage capacitor 206 (i.e., xe2x80x9cHV capxe2x80x9d). When in operation, the power source 140 provides power through the transformer 204 to charge the HV cap 206. The HV cap 206 stores the required voltage to be administered on the command of the operator or a controller 106 shown in FIG. 3. The HV cap 206 is typically a 105 xcexcf capacitor, and is capable of delivering a charge of 2100 volts to the patient through terminals 208 to the paddles 20 shown in FIG. 3. After discharge, the HV cap 206 is then recharged by the power source 140 if there is a continued need for defibrillation treatment.
A second type of defibrillator is an internal defibrillator. Internal defibrillators use a similar process for charging an HV cap. As shown in FIG. 5, an internal defibrillator 300 uses a power source 310 to charge a high voltage delivery device 320, which is a similar structure to the high voltage delivery device 108 shown in FIG. 4. The controller 330 controls the discharge of the high voltage delivery device 320 through the heart in order to regulate the rhythm of the heart. Where multiple capacitors are used in the high voltage delivery device 320, the high voltage delivery device 320 further includes an H-bridge in order to selectively provide shocks from the individual capacitors to the patient. In addition, the power source 310 is often a battery. An example of one such known internal defibrillator is found in U.S. Pat. No. 6,035,235 to Perttu et al.
A drawback to the conventional defibrillator designs, both external and internal, is the need for larger power sources to charge the HV cap in order to provide the necessary shock. For certain external defibrillators, especially those used in clinics, a line voltage can be supplied instead of a battery. However, such line sources limit the portability of these defibrillators when used in confined spaces.
A further problem encountered during the use of a defibrillator device is how to discharge or otherwise dissipate energy from the high voltage delivery device when the stored energy is not to be applied to a patient. As shown in FIG. 6, a common solution is to employ a dump resistor 400. In essence, the voltage from a high voltage delivery device 200 is dissipated as heat by the dump resistor 400, which is basically a large resistor. A problem encountered with this energy dissipation device is that it releases large amounts of heat. Such releases, especially if repeated in a short time, could damage the defibrillator.
An embodiment of the present invention has a defibrillator comprising a power source, a low impedance high capacitance double layer capacitor that stores energy from the power source, and a high voltage capacitor that stores energy provided the double layer capacitor, and discharges the stored energy to a patient.
In another embodiment of the present invention, the high voltage capacitor stores energy provided jointly by the double layer capacitor and the power source.
In another embodiment of the present invention, the defibrillator is located internal to a patient.
In another embodiment of the present invention, a set of leadless paddles or pads houses the high voltage capacitor and the double layer capacitor in order to defibrillate the patient without leads.
In another embodiment of the present invention, a method of charging a high voltage capacitor in a defibrillator is provided that includes supplying energy to a low impedance high capacitance double layer capacitor using a power source during a first time, and supplying energy from the low impedance high capacitance double layer capacitor to the high voltage capacitor during a second time.
In a yet further embodiment of the present invention, a method of administering a charge from a defibrillator to a patient is provided, including supplying energy to a low impedance high capacitance double layer cap using a power source during a first time, supplying energy from the low impedance high capacitance double layer cap to the high voltage capacitor during a second time, and discharging the high voltage capacitor to administer the charge to the patient.